1. Field of the Invention
The present invention relates generally to electrical safety devices. More particularly the invention concerns an adapter unit comprising a moisture resistent housing within which is carried an improved, self testing ground line fault interrupter device. The improved device is electrically interconnected with a connector carried externally of the adapter housing so that the unit can be plugged directly into a standard duplex outlet of an existing circuit.
2. Discussion of the Prior Art
The possibility of serious injury which is inherent in the operation of electrical systems has led to the design of various types of protective devices. Among these are the class of electrical apparatus which has come to be known as line fault, or ground fault circuit interrupters (GFI). In general, such devices sense a condition in a line carrying electrical current which indicates a presently or imminently dangerous condition, such as the presence of a current path other than the intended path of normal operation. Response to the sensed dangerous condition typically results in opening the line, that is interrupting the circuit, between the source of power and the load.
In the past GFI equipment has been designed for mounting in a conventional circuit breaker panel box at the input to the electrical distribution system of a building. .More recently GFI circuitry has been incorporated in portable boxes or housings having outwardly extending receptacle blades or prongs enabling detachable interconnection of the device with standard duplex outlets. U.S. Pat. No. 4,079,344 issued to Laubin, et al is exemplary of this latter type device.
As a general rule the prior art GFI devices include means for testing the operability of the device. Typically such devices are provided with manually activated "test" and "reset" switches which are operable when the device is interconnected within the circuit to test the integrity of the GFI device. One such prior art device is disclosed in U.S. Pat. No. 4,568,997 issued to Bienwald et al.
A substantial drawback of many of the portable prior art GFI devices is that the device is capable of conducting an electrical current even though it is defective and incapable of sensing a dangerous condition and properly interrupting the circuit. Accordingly, if the operator fails to test the device before using it, the device may appear to be functioning properly, but in fact offers no protection at all for a dangerous fault condition which may exist.
The improved apparatus of the present invention overcomes this serious drawback of the prior art devices by providing circuitry which automatically tests the device when it is plugged in to the house circuit by generating a simulated fault condition at the start of operation. With this unique construction, the device is automatically tested each time it is plugged into a duplex outlet without the operator performing any type of manual test. The device also includes the normal "test" and "reset" capability so that it can also be manually tested at any time.